Bonded piston seal (BPS, including piston seals, balance dams, drum seals, etc.) of rubber lip vulcanization-bonded type for use in clutch connection inside automatic transmissions (AT) of vehicles such as automobiles, etc. generally comprises a metal ring undergoing oil-hydraulic working (reciprocal motions) inside the automatic transmissions and a rubbery elastomer seal vulcanization-bonded to the metal ring, where the metal ring typically has a bonding site for vulcanization-bonding the rubbery seal, and also a sliding site along which a mating seal member (such as O ring, a rubber lip, or the like, as provided on the AT housing side).    Patent Literature 1: JP-A-2002-139155
An adhesive is used to vulcanization-bond the seal to the metal ring. The adhesive has a rust-preventive effect on the metal ring when laid thereon, so the adhesive is generally applied by “full dipping” and thus applied to the entire exposed surface of the ring except the bonding site.
However, from the viewpoint of the working characteristics of bonded piston seal is regarded as important, on the other hand, fluctuations (i.e. instability) in the frictional resistance caused by sliding along the mating seal member must be suppressed, and thus the adhesive layer formed on the sliding site, which is a cause for the fluctuations, must be removed by cutting. This cutting removal step has been so far carried out as one step of the process.
The step of removing the adhesive layer can be carried out specifically by cutting work, where the surface roughness must be smaller to suppress the abrasion of the mating seal member, and furthermore a higher dimensional precision is required for cutting to suppress the fluctuations in contact state (contact interference) of the mating seal member, so the cutting work requires much time and labor, resulting in a problem of higher processing cost than usual.
Furthermore, the cutting work is carried out as the final step following the step of adhesive application and the step of vulcanization molding, so prevention of rubber seal from any damages by chips, removal of attached foreign matters by washing, and necessary inspection for quality confirmation, etc. are required for the seal security, resulting in much more time and labor. This is a problem of increased cost.
Besides the afore-mentioned type of bonded piston seal provided the bonding site and the sliding site on a metal ring, the bonded piston seal has another type of bonding sites provided on both inside and outside peripheries of a metal ring (type of vulcanization-bonded seals on both inside and outside peripheries of a metal ring), or a further type of a bonding site provided only on one of inside or outside peripheries of a metal ring (type of a vulcanization-bonded seal on one of inside or outside peripheries of a metal ring and a sliding site provided on the other periphery or not, and this type can be used often particularly as a balance dam). When the adhesive is applied to the metal ring by full dipping, irrespective of the type, the amount of the adhesive as used is inevitably increased. An organic solvent is used in the most of adhesives, so the evaporative scattering of the solvent would cause an environmental problem.    Patent Literature 2: JP-A-2003-56717    Patent Literature 3: JP-A-11-257374